P0977

P0977 is the Shift Solenoid B Control Circuit High — the TCM commands SS-B and reads voltage stuck high (open circuit, no current flowing when current was expected). The cause is an open wire, an open solenoid winding, a pushed-back pin at the case connector, or a TCM driver gone open-circuit. Cheapest-first: pull the case connector and inspect for pushed-back terminals or green-fuzz corrosion from ATF wicking up the pins — this is the #1 cause and costs zero to find. Ohm SS-B at the case connector pin-to-pin: 8-30 ohms is the typical spec (19-31 ohms GM 4L60E, 9-16 ohms Ford 4R75W, 11-15 ohms Chrysler 545RFE pack, 10-15 ohms Toyota A340/A750). Infinite ohms = open winding, solenoid (or pack) replacement. In-spec ohms at the case = the open is upstream, back-probe the harness between TCM and case connector and ohm each conductor end-to-end (wire resistance should be under 5 ohms on a short run; anything higher means a corroded splice, pushed pin, or break). Ohms-to-ground on each pin should be >100k ohms (floating). Active current at full command should be 0.5-1.5 A — read zero current with the driver commanded on and the open is confirmed. Expensive-misdiagnosis caveat: on Chrysler 545RFE/68RFE intermittent or stable P0977 is frequently the result of an internal pack solder-joint failure that thermally cycles open — passes cold, opens hot, returns at temp — and only full solenoid-pack replacement clears it. RAM trans techs at AAMCO and independent shops aggregate this as one of the highest-frequency 545RFE/68RFE codes in the 70k-150k mile band, and chasing individual wires on this trans is a known waste of customer money.

Vehicle-specific patterns: 1996-2007 GM 4L60E/4L65E throws P0977 from case-connector pin-fit loss after repeated unplugging during routine fluid service — GM service guidance is to replace the case-connector body rather than just spraying contact cleaner, $40-80 part. 2003-2010 Dodge Ram 1500/2500 with the 545RFE and 2007-up 68RFE sets P0977 as a near-certain pack-failure indicator in the 70,000-150,000 mile band — pack replacement $500-900 parts plus labor at independents per AAMCO/RepairPal aggregated cost data. 2007-2013 Ram HD with the Aisin AS69RC throws P0977 from a documented internal pigtail solder-joint break inside the valve-body solenoid carrier, valve-body R&R required, $800-1,400. 2001-2010 GM HD with the Allison 1000 (LCT1000) sets the equivalent open-circuit from PCS-2/PCS-3 wire-break at the case-flange ridge chafe location — repair the wire before condemning the solenoid, per Allison service guidance. Estimated repair: $300 to $1,500.